1. Field of the Invention
The present invention relates to such an electronic control apparatus for an engine of a vehicle as is provided with a central processing unit (CPU) for controlling a throttle valve which is disposed in an intake pipe of the engine, by outputting an opening degree signal to an actuator which operates to open or close the throttle valve.
2. Description of Related Art
In a conventional electronic control apparatus for an engine of a vehicle, a CPU for throttle valve control is provided with a large number of input ports for inputting detected signals from an acceleration sensor which detects the amount of depression of an accelerator and various other sensors which detect the engine conditions, as well as with a high-accuracy or high-resolution analog/digital (A/D) converting portion or converter which converts each of the detected signals. It is so arranged, inside this CPU for throttle valve control, that an opening degree signal which is to be output to the actuator is computed based on the detected signals which have been converted in the A/D converter.
In case where the engine is of an electronic fuel injection type, the electronic control apparatus is provided with a CPU for fuel control which controls the amount of fuel to be supplied to the engine. This CPU for controlling the fuel inputs detected signals from an acceleration sensor which detects the amount of depression of an accelerator as well as from various other sensors which detect the engine conditions. Based on these detected signals the amount of fuel to be supplied is computed. For that purpose, this CPU is provided with an input member which has many input ports and a high-accuracy A/D converter which converts the detected signals to digital signals. In order to process these converted signals at a high speed, the CPU itself has a high capacity.
In the above-described conventional arrangement, not only the CPU for fuel control but also the CPU for throttle valve control has to be provided with the input member which has many input ports and the high-resolution A/D converter. Further, the CPU for throttle valve control must also be of a high-capacity or high-performance one. As a result, the cost of the electronic control apparatus becomes expensive.
In view of the above-described disadvantages, the present invention has an object of providing at a smaller cost such an electronic control apparatus for an engine of a vehicle as is provided with a capacity equivalent to that of a conventional one.
According to one aspect of the present invention, the foregoing and other objects are attained by an electronic control apparatus for an engine of a vehicle, the apparatus having a first CPU for fuel control which controls the amount of fuel to be supplied to the engine and a second CPU for throttle valve control which outputs a driving signal to an actuator which operates to open or close a throttle valve disposed in an intake pipe to the engine, the apparatus comprising: an opening degree computing member which is provided in the first CPU to compute an opening degree of the throttle valve based at least on an amount of depression of an accelerator and then to output a result thereof as an opening degree signal; the first CPU and the second CPU being connected together by a communication line which transfers the opening degree signal from the opening degree computing member from the first CPU to the second CPU.
Among the opening degree signals to determine the driving signal to the actuator, those which are based on the amount of depression of the accelerator, or the like are computed by using the same data as for the computation, in the first CPU, of the amount of fuel supply. By letting this computation for obtaining the opening degree signal be carried out in the first CPU and then transferring the opening degree signal, which is the result of the computation, to the second CPU, the input ports for the second CPU may be small in number. Further, the second CPU needs neither be provided with a high-resolution A/D converter nor be required to have a high performance or capacity. It becomes thus possible to use, as the second CPU, a CPU which is cheaper than a conventionally used one.
In a preferred embodiment, there is sometimes provided a constant speed computing and controlling member which computes that opening degree of the throttle valve which causes the vehicle to travel at a constant speed to be set by a vehicle speed setting signal. Since it is sufficient for this constant speed computing and controlling member to compute the opening degree of the throttle valve based on a vehicle speed signal which has already been pulse-inputted in the first CPU, it does not require a high-resolution or high-capacity A/D converter for inputting the opening degree of the throttle valve. Therefore, it is preferable to incorporate this constant speed computing and controlling member into the second CPU in order to determine the above-described driving signal based on a computing result of the constant speed computing and controlling member and on the opening degree signal from the first CPU.
Further, in order to detect any abnormality which may occur in the first CPU, it is preferable to employ the following arrangement. Namely, the signal representing the amount of depression of the accelerator is also input to the second CPU. Based on this signal of amount of depression of the accelerator, a rough opening degree signal is obtained. Based on this rough opening degree signal, a judgement is made in the second CPU as to whether the opening degree signal being transferred from the first CPU is abnormal or not.
If, like in the conventional art, the opening degree of the throttle valve based on the amount of depression of the accelerator is computed only by the CPU for throttle valve control, there is the following disadvantage. Namely, when there has occurred an abnormality such as a trouble or the like in a throttle valve control system inclusive of the CPU for throttle valve control, it becomes impossible to control the opening degree of the throttle valve in interlocking with the operation by the driver of the accelerator.
In preparation for such an abnormality the following solution may be considered. Namely, aside from the throttle valve control system inclusive of the CPU for throttle valve control, there is provided a means for fixing the opening degree of the throttle valve to a predetermined fixed value which is set in advance so that the vehicle may be kept travelling. However, if the opening degree of the throttle valve is fixed in the manner as described above, the vehicle speed does not vary even if the accelerator were depressed, with the result that the driver's intention cannot be reflected on the vehicle's travelling.
In order to increase the redundancy in respect to an abnormality in the throttle valve control system, according to another aspect of the present invention, there is provided an electronic control apparatus for an engine of a vehicle, the apparatus having a CPU for throttle valve control for outputting an opening degree signal to an actuator which operates to open or close a throttle valve disposed in an intake pipe to the engine, the apparatus comprising: a CPU for opening degree computation which computes an opening degree of the throttle valve based at least on an amount of depression of an accelerator and then outputs a result thereof to the CPU for throttle valve control as an opening degree signal; the CPU for throttle valve control comprising: computing means for alternative opening degree computation which computes an alternative signal to the opening degree signal based on the amount of depression of the accelerator; a memory member which memorizes the opening degree signal from the CPU for opening degree computation; and alternative driving means which outputs the alternative signal to the actuator as an opening degree signal when the memory member is abnormal.
In still another aspect of the present invention, there is provided an electronic control apparatus for an engine of a vehicle, the apparatus having a CPU for throttle valve control by outputting an opening degree signal to an actuator which operates to open or close the throttle valve disposed in an intake pipe to the engine, the apparatus comprising: a CPU for opening degree computation which computes an opening degree of the throttle valve based at least on an amount of depression of an accelerator and then outputs a result thereof to the CPU for throttle valve control as an opening degree signal; the CPU for throttle valve control comprising: computing means for alternative opening degree computation which computes an alternative signal to the opening degree signal based on the amount of depression of the accelerator; a memory member which memorizes the opening degree signal from the CPU for opening degree computation; and auxiliary driving means which judges, based on the alternative signal, an abnormality of the opening degree signal which is stored in the memory member and outputs to the actuator an alternative opening degree signal when the opening degree signal is abnormal.
As described above, by providing the CPU for opening degree computation (it is not necessarily limited to the CPU for fuel control as described above) aside from the CPU for throttle valve control, it becomes possible, when an abnormality has occurred in the memory member which is contained inside the CPU for opening degree computation or the CPU for throttle valve control, to output to the actuator the alternative signal to be computed inside the CPU for throttle valve control. As a result, it becomes possible to operate and control the opening degree of the throttle valve depending on the operation of the accelerator.
In case an abnormality has occurred in the CPU for throttle valve control or the actuator and, as a result, the throttle valve can no longer be operated, the speed of rotation of the engine can be limited to a certain degree by limiting the amount of fuel supply. However, the driver's intention cannot be reflected by simply limiting the speed of rotation of the engine, and there is a possibility of the engine to race. It is therefore preferable to prevent the engine from racing by changing, by means of a separately provided CPU for auxiliary control, the upper limit restriction value of a speed of engine rotation and, at the same time, to change this upper limit restriction value based on an amount of depression of the accelerator so that the vehicle speed can be varied in interlocking with the driver's operation of the accelerator.